Question

If 5x - 3y = 7 and 2y - 4x = 3, then 2x - 2y =

Answer 1

i have the answer it's 20 but I need to know the steps

Answer 2

5x - 3y = 7 ===> (4)
-4x + 2y = 3 ===>(5)
-----------------
20x - 12y = 28 (result of multiplying by 4)
-20x + 10y = 15 (result of multiplying by 5)
----------------add
-2y = 43
y = - 43/2

-4x + 2y = 3
-4x + 2(-43/2) = 3
-4x - 86/2 = 3
-4x - 43 = 3
-4x = 3 + 43
-4x = 46
x = - 46/4 which reduces to - 23/2

5x - 3y = 7
5(-23/2) - 3y = 7
- 115/2 - 3y = 7
-3y = 7 + 115/2
-3y = 14/2 + 115/2
-3y = 129/2
y = (129/2) / -3
y = 129/2 * -1/3
y = -129/6 which reduces to - 43/2

lets check our answers before we go any further
5x - 3y = 7
5(-23/2) - 3(-43/2) = 7
- 115/2 + 129/2 = 7
14/2 = 7
7 = 7 (correct)

so we know that x = -23/2 and y = -43/2

2x - 2y =
2(-23/2) - 2(-43/2) =
- 46/2 + 86/2 =
40/2 = 20

Answer 3

hey why didn't u just use the system of equations?

Answer 4

I used the system of equations and solved for x and y...through elimination

Answer 5

you could also use the system of equations and solve for x and y through substitution

Answer 6

either way, you are going to get fractions as x and y.

Answer 7

damn.... okay i got it now thank you so much